BIOPHYSICS

discipline concerned with the application of the principles and methods of physics and the other physical sciences to the solution of biological problems. The relatively recent emergence of biophysics as a scientific discipline may be attributed, in particular, to the spectacular success of biophysical tools in unravelling the molecular structure of deoxyribonucleic acid (DNA), the fundamental hereditary material, and in establishing the precisely detailed structure of proteins such as hemoglobin in order that the position of each atom may be known. Biophysics and the intimately related subject molecular biology now are firmly established as cornerstones of modern biology. discipline concerned with the application of the principles and methods of the physical sciences to biological problems. The major areas of biophysics deal with biological function when the function depends on physical agents such as electricity (in nerves) or mechanical force (in muscles), the interaction of living organisms with physical agents such as light or sound or ionizing radiations (e.g., X rays), and interactions between living things and their environment as in locomotion (swimming, flying, etc.), navigation, and communication. Sophisticated methodology and instrumentation are crucial in biophysics. In molecular biophysics, for example, X-ray diffraction and a sedimentation technique carried out with the ultracentrifuge have been among the most productive. These have made possible precise descriptions of the structure and properties of macromolecules found in animals and plants. Moreover, with the aid of electron microscopy and nuclear magnetic resonance, the molecular configuration and bonding of the principal constituents of cell membranes and chromosomes have been determined. Physicists and physiologists have been aware of the biological effects of electric currents since Luigi Galvani's discovery of bioelectricity in the 18th century, and much work in biophysics has been concerned with the role of electric pulses in the conduction of information by nerves and in initiating muscular contraction. The generation of force by contracting muscle is also studied by biophysicists. Biophysical studies of the senses have made much progress in the areas of vision and hearing. The use of light by plants is also investigated by biophysicists as the process of photosynthesis starts as a physical interaction even though it later develops through a chemical chain. Study of the effects of ultraviolet light is an extension of the study of the effects of visible light. No form of life is adapted to use ionizing radiations, but these constantly impinge on living organisms in the form of cosmic rays and naturally occurring radiations from uranium, radium, etc. The development of man-made sources of these radiations in the form of X-ray machines, nuclear-power reactors, and isotopes used as tracers, as well as nuclear weapons, has been the spur for extensive research into their biophysical effects. There have been studies of the biological effects of lower-energy electromagnetic radiations (radio and radar waves), and of intense beams of infrared and visible light such as may be produced by lasers. Locomotion presents one of the more complicated biophysical problems. The ways in which birds fly and fish swim involve complex considerations of aerodynamics and hydrodynamics, respectively. Mathematical expression of human and animal locomotion is formidably complex. Animal movement also requires navigation, and this has revealed unexpected biophysical patterns, ranging from the use of ultrasonics by bats, to a kind of low-frequency radar used by certain fish, to the use of magnetic fields by pigeons and polarization of sunlight by bees. Additional reading S.A. Wainwright et al., Mechanical Design in Organisms (1982), relates general principles. Two elegant books on the physics of operating systems in animals and plants are Steven Vogel, Life's Devices: The Physical World of Animals and Plants (1988), a general account of the basic rules governing these systems, and Life in Moving Fluids: The Physical Biology of Flow, 2nd ed. rev. and expanded (1994), on fluid dynamics as they pertain to a variety of organisms, both engagingly written. Additional studies are Edward L. Alpen, Radiation Biophysics (1991), for advanced undergraduates and graduate students; Struther Arnott, D.A. Rees, and E.R. Morris (eds.), Molecular Biophysics of the Extracellular Matrix (1984), an examination of proteoglycans and glycosaminoglycans; Thomas H. Dawson, Engineering Design of the Cardiovascular System of Mammals (1991), an illuminating reference source; and Camillo Peracchia, Biophysics of Gap Junction Channels (1991), a solid historical treatment of the concept. The Editors of the Encyclopdia Britannica